Papers by Author: Rosario Ceravolo

Abstract: Several nonlinear system identification methods have been presented in the past, such as the Extended Kalman Filter, the H filter and the Sequential Monte Carlo methods. One of the most promising ones is the Unscented Kalman Filter (UKF) recently proposed for the on-line identification of structural parameters. In the present study the UKF is proposed to the purpose of the nonlinear identification of a new prototype of rolling-pendulum tuned vibration absorber which, relying on an optimal three-dimensional guiding receptacle, can simultaneously control the response of the supporting structure along two orthogonal horizontal directions. Unlike existing ball vibration absorbers, mounted on spherical recesses and used in axial-symmetrical structures, the new device can be bidirectionally tuned to both fundamental structural modes even when the corresponding natural frequencies are different, by virtue of the optimum shape of the rolling cavity. Based on preliminary numerical simulations, the UKF is shown to be effective in identifying the structural parameters of the new device and particularly the nonlinear rolling friction dissipation mechanism at the interface between the ball bearing and the rolling surface.

Abstract: The evaluation of the safety and the estimation of the remaining service life of existing structures need a thorough knowledge of the effective operational conditions, achievable implementing a health monitoring system. The measured quantities, if opportunely chosen, allow to follow the evolution of the structural behavior in the lifetime and to recognize the occurrence of damages. Hence the collected data can be considered as symptoms and used to assess the reliability and the prognosis of the monitored structure. This paper presents the application of symptom-based reliability formulation to a real case study: a set of precast bonded post-tensioned concrete bridge beams, recently dismounted after a service life of 50 years. Both static and dynamic tests were carried out at the aim of evaluating the residual load-bearing capacity and investigating the effects of deterioration on their dynamic properties. The experimental results of test campaigns have been used as symptoms in order to estimate the reliability function of the beams and the evolution of their resistance in time.

Abstract: A scaled model of a two-span masonry arch bridge has been built in order to investigate the effect of the central pile settlement due to riverbank erosion. The bridge model has been equipped with different Non Destructive Testing (NDT) instruments and subjected to incremental settlement of the pier. The evolution of the pier scour has been investigated experimentally by means of a hydraulic model and reproduced accordingly. The numerical interpretation of damage, carried out by finite element analyses, has been compared with the results of the Acoustic Emissions (AE) monitoring. Several ultrasonic emissions have been detected and main damage source areas have been localized.

Abstract: The erosion of the river bed material at bridge pier foundation produced by scour events is one of the main causes of the observed masonry bridges failures and collapses. Foundation settlements and rotations derived from the reduction of the footprint under the piers threaten masonry arch bridges integrity more than any gravity load. The resulting effect on the structure is the development of cracking mechanisms on the arches which may affect the dynamic behaviour of the whole bridge. A scaled experimental model of a masonry arch bridge has been built in the laboratory of the Dep. of Structural Engineering at the Politecnico di Torino. The aim was to better understand scour damage scenario and to identify early structural symptoms of pier erosion. A preliminary dynamic identification is carried out on the intact structure and a comparison with the FEM results is performed. The set of identified modal parameters is adopted as the reference system that will be compared with those acquired after the application of damage of increasing extent.

Abstract: The identification of non-linear systems is an important topic in structural health monitoring of structures undergoing non-stationary behavior. In general, a non-linear or hysteretic response is typical for buildings, bridges, dampers and structural elements not only as a consequence of strong excitations (i. e. earthquake), but also for low to medium loading levels, due to the constitutive behavior of structural elements or joints. This paper focuses on the non-linear identification of a RC beam-column joint, modeled as a SDoF system, subjected to non-stationary loading: the technique used entails the definition of proper instantaneous estimators of the system dynamic properties by using a linear time-varying approximation of the actual system dynamics and representing the structural response in the joint time-frequency domain.

Abstract: This paper presents a technique for identification of non-linear hysteretic systems subjected to non-stationary loading. In the numerical simulations, a Bouc-Wen model was chosen for its ability to represent the properties of a wide class of real hysteretic systems. The parameters of the model are computed instantaneously by approximating the internal restoring force surface through an “ad hoc” polynomial basis. Instantaneous estimates result from time-varying spectra of the response signals. A numerical application of interest to earthquake engineering is finally reported.

Abstract: In structural engineering applications a sufficient quantity of experimental data to be able to achieve a consistent estimate of nonlinear quantities is seldom available: this applies in particular when the structures are to be tested in situ. This report discusses the definition of instantaneous estimators to be used in the dynamic identification of invariant nonlinear systems on the basis of Short-Time Fourier Transform representation of excitation and system’s response and within the framework of a Volterra series representation of the input/output relationship. An estimation of the parameters of a dynamic system can be worked out from the evolution of such instantaneous estimators.